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Hello everyone,

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This is a more generic request for help that impacts everything I am doing in my shack with my older Tektronix 200 Mhz analog o-scope. Specifically, I have been seeing a "noise" in the last few weeks that I don't recall seeing before...although it is possible it was there and I just was not seeing it because I was looking at larger signals. Not sure about that.

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But here is what I am seeing... in connection with developing a 30M local oscillator for a homebrew design... when I view the intended signal on my scope at ~10 Mhz, I am seeing superimposed on that sine wave a lower level signal that appears to have 8 periods for every period of the main signal. It's low level but very noticeable on the scope. That would put the noise at around 80 Mhz.

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At first I thought I had an internal problem with my scope, or my probes, or... whatever. But I have now seen the signal with a second scope and several different probes. Then thinking it was some weird product of my oscillator design, I looked at a signal from a signal generator, and saw the exact same noise. Multiple probes, two different scopes, and a couple different signal sources, and I still see it.

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So now I suspect some source of noise in the 80 Mhz range in my shack or neighborhood that my mesaurement system is picking up. I have no clue what this would be. Any thoughts? Has anyone else ever experienced something like this?

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If we need to find an excuse for this to be addressed in this group, I recently built a QCX+ for 30M as my "benchmark" for my own design comparison... LOL... hopefully that's good enough.

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73 & TIA,

Joel W9JFK

Maybe a local FM station.?? When I run the FFT function on my scope, I pick up a signal of a station about 20 miles away.? For me it is very weak so I don't see it with more normal scope usage.

I had a USB mini computer that would generate noise in that range. I found the problem by walking around the house with a pocket shortwave radio, and in the process also found several wall warts that were generating noise.?

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73, Dan - W2DLC

That's a good point. I am going to try and narrow down the signal to something more precise than "in the 80 Mhz. range" and then see what I can detect with other means.

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Any other thoughts from anyone else appreciated but yeah, local FM seems possible.?

Yeah, definitely possible in this world of RF congestion... I definitely plan to walk around the house with a small receiver and see what I can find. Thanks!

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Joel W9JFK

As someone else mentioned it could be a nearby FM station. ?I do a lot of technical troubleshooting at a ham friends house who live close to an FM broadcast station (probably within a mile or two of the transmitter), and we have often observed the FM stations signal on my scope when measuring various systems at his house. ?I have a Rigol scope and have used both the internal bandwidth limit option (20 MHz low pass filter) as well as the digital filter option at times to deal with it.

On Tue, Oct 15, 2024 at 10:59 AM, Joel W9JFK wrote:

and then see what I can detect with other means.

This seems like the perfect excuse to obtain a TinySA Ultra: ?

73, Don N2VGU

If you can convince my wife of that, I would bite LOL... I probably will anyway ;)